Effects of glyphosate and foliar amendments on activity of microorganisms in the soybean rhizosphere

A field study was conducted to determine the effects of glyphosate on microbial activity in the rhizosphere of glyphosate-resistant (GR) soybean and to evaluate interactions with foliar amendments. Glyphosate at 0.84 kg ae ha^{? 1} was applied GR soybean at the V4–V5 development stages. Check treatments included a conventional herbicide tank mix (2003 study only) and no herbicides (hand-weeded). Ten days after herbicide application, a commercially available biostimulant and a urea solution (21.0% N) were applied to soybean foliage at 33.5 mL ha^{? 1} and 9.2 kg ha^{? 1}, respectively. Soil and plant samples were taken 0, 5, 10, 15, 20 and 25 days after herbicide application then assayed for enzyme and respiration activities. Soil respiration and enzyme activity increased with glyphosate and foliar amendment applications during the 2002 growing season; however, similar increases were not observed in 2003. Contrasting cumulative rainfall between 2002 and 2003 likely accounted for differences in soil microbial activities. Increases in soil microbial activity in 2002 suggest that adequate soil water and glyphosate application acted together to increase microbial activity. Our study suggests that general soil microbial properties including those involving C and N transformations are not sensitive enough to detect effects of glyphosate on rhizosphere microbial activity. Measurements of soil-plant-microbe relationships including specific microbial groups (i.e., root-associated Fusarium spp.) are likely better indicators of impacts of glyphosate on soil microbial ecology.     

Functional autotrophy of Heteroxenia fuscescens (Anthozoa: Alcyonaria): carbon assimilation and translocation of photosynthates from symbionts to host

The association of the alcyonarian Heteroxenia fuscescens (Ehrb.) with its cytosymbiotic algae shows structural and physiological adaptations optimizing the living together of the two partners as one functional unit. To enhance the energetic contribution of the autotrophic partner, the organization of the heterotrophic partner bears typical plant-like imprints. Up to 20% of the inorganic C photosynthetically fixed was translocated to the host (=2 mg C mg d.w.^-1 d^-1). This net C gain by the host is used for anabolic purposes including the deposition of storage material. Especially the wax-esters and triglycerides of the host-in contrast to those of the symbionts-were intensively labelled. The in-vivo ¹⁴C-fixation of zooxanthellae is more than double the in-vitro fixation. In both symbionts and host, the lipids show the highest relative ¹⁴C-incorporation. In particular the polyol component was strongly labelled. After 120 min of continuous incubation, approximately 40 labelled intracellular metabolites were detectable in the ethanol/water soluble fractions of zooxanthellae. Glycerol is the main low-molecular weight carbohydrate being transferred. This is corroborated by the deacylation of lipids of the host.     

Studies on 14CO2-assimilation in marine rhodophyceae

Experiments on enzymatic (in vitro) and in vivo CO₂-fixation using a variety of marine Rhodophyceae such as Porphyra umbilicalis (L.) J.Ag., Rhodomela confervoides (Huds.) Silva, Corallina officinalis L. and Chondrus crispus Stackh. revealed that carbon assimilation in the Rhodophyceae is almost exclusively performed by photosynthesis via ribulose-1, 5-di-phosphate carboxylase, whereas light-independent CO₂-fixation via -carboxylation by phosphoenolpyruvate carboxykinase scarcely exceeds 1% of the total carbon fixation potential of the plants. Activity of phosphoenolpyruvate carboxylase could not be detected. With respect to the main accumulation products of photosynthetic CO₂-fixation, the Rhodophyceae investigated are not uniform: Corallina officinalis L., Rhodymenia palmata (L.) Grev., and Gigartina stellata (Stackh.) Batt. have been found to accumulate ¹⁴C in the neutral compound floridoside (=2-O-glycerol--D-galactopyranose), whereas Delesseria sanguinea (Huds.) Lamour., Ceramium cubrum (Huds,) C.Ag., and Rhodomela confervoides (Huds.) Silva, representing members of the Delesseriaceae, Ceramiaceae and Rhodomelaceae, respectively, do not photosynthesize floridoside, but show intense ¹⁴C-labelling in an acidic constituent, mannosidoglycerate (= digeneaside). This compound is reported for the first time as a rapidly ¹⁴C-labelled and accumulated photosynthate in a variety of red algal species exclusively belonging to the Ceramiales.     

Evaluation of variance approximation techniques for non-linear photosynthesis—irradiance models

Parameters derived from photosynthesis-irradiance (P-I) models, although often empirical in nature, are useful indicators of the photoadaptive state of phytoplankton in culture and in situ. However objective criteria for determining significant changes in P-I curves are rarely provided, because confidence intervals for parameters of non-linear models are not estimated easily. Examination of least-squares residuals in parameter space and Monte Carlo approaches have been used to estimate confidence regions around parameter values, but the computationally intensive nature of these methods has prevented their routine application. We present an alternative method of estimating confidence intervals for parameters of P-I curves that runs quickly on a microcomputer and is easily combined with common parameter-estimation routines. This algorithm was tested using a 3-parameter P-I model and curves describing a wide range of photoadaptive states, with different numbers of observations and different amounts of inherent variability. The method produced results comparable to the Monte Carlo technique. This analysis makes it possible to specify the sample size required to define parameters with acceptable confidence as a function of data variance and photoadaptive state. In most reasonable situations, 25 observations are sufficient.     

Stimulated rhizodegradation of atrazine by selected plant species

The efficacy of vegetative buffer strips (VBS) in removing herbicides deposited from surface runoff is related to the ability of plant species to promote rapid herbicide degradation. A growth chamber study was conducted to compare C-atrazine (ATR) degradation profiles in soil rhizospheres from different forage grasses and correlate ATR degradation rates and profiles with microbial activity using three soil enzymes. The plant treatments included: (i) orchardgrass ( L.), (ii) smooth bromegrass ( Leyss.), (iii) tall fescue ( Schreb.), (iv) Illinois bundle flower (), (v) perennial ryegrass ( L.), (vi) switchgrass ( L.), and (vii) eastern gamagrass (). Soil without plants was used as the control. The results suggested that all plant species significantly enhanced ATR degradation by 84 to 260% compared with the control, but eastern gamagrass showed the highest capability for promoting biodegradation of ATR in the rhizosphere. More than 90% of ATR was degraded in the eastern gamagrass rhizosphere compared with 24% in the control. Dealkylation of atrazine strongly correlated with increased enzymatic activities of β-glucosidase (GLU) ( = 0.96), dehydrogenase (DHG) ( = 0.842), and fluorescein diacetate (FDA) hydrolysis ( = 0.702). The incorporation of forage species, particularly eastern gamagrass, into VBS designs will significantly promote the degradation of ATR transported into the VBS by surface runoff. Microbial parameters widely used for assessment of soil quality, e.g., DHG and GLU activities, are promising tools for evaluating the overall degradation potential of various vegetative buffer designs for ATR remediation.     

Defecation by Salpa thompsoni and its contribution to vertical flux in the Southern Ocean

Measurements of the defecation rate of Salpa thompsoni were made at several stations during two cruises west of the Antarctic Peninsula in 2004 and 2006. Rates were quantified in terms of number of pellets, pigment, carbon and nitrogen for a wide size range of both aggregate and solitary salps. Measured defecation rates were constant over several hours when salps were held at near-surface conditions from which they had been collected. The defecation rate per salp increased with both salp size and the ambient level of particulate organic matter (POM) in the upper water column. The weight-specific defecation rate ranged between 0.5 and 6% day⁻¹ of salp body carbon, depending on the concentration of available particulate matter in the water. Carbon defecation rates were applied to biomass estimates of S. thompsoni to calculate daily carbon defecation rates for the populations sampled during the two cruises. Dense salp populations of over 400 mg C m⁻² were calculated to produce about 20 mg C m⁻² day⁻¹, comparable to other major sources of vertical flux of organic material in the Southern Ocean. Measured sinking rates for salp fecal pellets indicated that the majority of this organic material could reach deep sediments within a few days, providing a fast and direct pathway for carbon to the deep ocean.     

Carbon metabolism and strobilation in Cassiopea andromedea (Cnidaria: Scyphozoa): Significance of endosymbiotic dinoflagellates

Scyphopolyps and scyphomedusae of Cassiopea andromeda Forskål (Cnidaria, Scyphozoa) containing dinoflagellate endosymbionts (zooxanthellae) were investigated for rates and pathways of carbon fixation. Photosynthesis by the algae, accounting for 80 and 15 mol C h^-1 on a dry weight basis in medusae and polyps, respectively, by far exceeds dark incorporation of inorganic carbon by the intact association. Photosynthetic carbon fixation is operated via C₃ pathway of carbon reduction. DCMU-treatment (1×10^-6 M and 1×10^-5 M) completely inhibits light-dependent carbon assimilation. Major photosynthates presumably involved in a metabolite flow from algal symbionts to animal tissue are glycerol and glucose. A total of 5–10% net algal photosynthate appears to be seleased in vivo to the host. This is probably less than the energy supply ultimately required for the nutrition of the polyps and medusae. The presence of zooxanthellae proved to be indispensable for strobilation in the scyphopolyps. However, photosynthesis by algal symbionts as well as photosynthate release is obviously not essential for the initiation of ephyrae as is shown by DCMU-treatment, culture in continous darkness, and aposymbiotic controls. It is therefore concluded that strobilation is supported, but not triggered by algal photosynthetic activity. The induction of strobilation thus seems to depend on a more complex system of regulation.     

Transmission of symbiotic dinoflagellates through the sexual cycle of the host scyphozoan Linuche unguiculata

Intracellular symbiotic dinoflagellates are associated with the tropical scyphozoan Linuche unguiculata (Swartz, 1788) throughout all stages of the host's life cycle. During sexual reproduction, eggs are released in mucus strands that contain symbiotic dinoflagellates. Fertilization and development take place externally in the water column. Epifluorescence and transmission electron microscopy showed that unfertilized eggs did not contain intracellular algae, but that infection of the developing embryo was generally successful by the 128-cell stage (10 h after fertilization at 23° C). However, experiments with artificially provided Cellufluor-labeled algae demonstrated that older embryos and planulae could be infected by algae through at least 24 h post-fertilization, indicating that the L. unguiculata symbiosis represents a semi-closed system. This novel mode of symbiont acquisition results in most sexually-produced offspring becoming infected with maternally-transmitted algae during early development, but allows for acquisition of non-maternally-provided algae later in development. Most of the algal symbionts during the early stages of embryonic and larval development are located within ectodermal cells. This is in contrast to the other life-cycle stages of L. unguiculata (i.e., scyphistoma, medusa, ephyra), where symbionts are found within the gastrodermis of the host.     

Effects of glyphosate and foliar amendments on activity of microorganisms in the soybean rhizosphere

A field study was conducted to determine the effects of glyphosate on microbial activity in the rhizosphere of glyphosate-resistant (GR) soybean and to evaluate interactions with foliar amendments. Glyphosate at 0.84 kg ae ha(-1) was applied GR soybean at the V4-V5 development stages. Check treatments included a conventional herbicide tank mix (2003 study only) and no herbicides (hand-weeded). Ten days after herbicide application, a commercially available biostimulant and a urea solution (21.0% N) were applied to soybean foliage at 33.5 mL ha(-1) and 9.2 kg ha(-1), respectively. Soil and plant samples were taken 0, 5, 10, 15, 20 and 25 days after herbicide application then assayed for enzyme and respiration activities. Soil respiration and enzyme activity increased with glyphosate and foliar amendment applications during the 2002 growing season; however, similar increases were not observed in 2003. Contrasting cumulative rainfall between 2002 and 2003 likely accounted for differences in soil microbial activities. Increases in soil microbial activity in 2002 suggest that adequate soil water and glyphosate application acted together to increase microbial activity. Our study suggests that general soil microbial properties including those involving C and N transformations are not sensitive enough to detect effects of glyphosate on rhizosphere microbial activity. Measurements of soil-plant-microbe relationships including specific microbial groups (i.e., root-associated Fusarium spp.) are likely better indicators of impacts of glyphosate on soil microbial ecology.     

BASSETT CREEK WATERSHED MODEL1

ABSTRACT: A synthetic hydrograph method was utilized in the development of a watershed model for a small urbanizing watershed. The model was applied to the watershed and the largest flood of record was accurately reproduced. Because the model would be utilized for design of flood control plans with complete urbanization, the method was also applied to an urbanized watershed and reproduced a measured event with good results. The method does not require extensive hydrologic data for its implementation, can be applied to watersheds in various stages of urbanization, and permits consideration of natural or potential floodwater storage.